Ajax post allways sends null parameter to web api controller

I use ajax call from mobile site to get and send data to a web api service. The get calls work fine but I can't make a post . In the web api controller, the parameter is allways null.  The ajax post properties  are : accept: 'text/json',

dataType : 'text'

contentType : 'text/json'

crossDomain : true

data: JSON.stringify(myObject)

 

 I try to pass a primitive parameter to the controller, the result is the same, no data sent

 

Environment : Visual Studio 2015 with Apache Cordova 

 

Help Please